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282 MORPHOLOGY AMD EVOLUTION
(6) The small sulcus lunatus corresponds to the large Affenspalte.
(7) Secondary sulci are more numerous.
\8) The cerebrum conceals the cerebellum more completely, and the latter shows a higher phase of evolution.
(9) Many greater complexities are the result of a larger neopallium.
(10) Some of the cranial nerves are smaller.
(11) The corpus callosurn is larger.
THE BRAIX IK THE GIBBONS (fig. 50).
The brain in the Gibbons is intermediate in its characters between those of the Cercopifchecidse, on the one hand, and those of the larger Simiidse on the other. Moreover it indicates in some ways the path pursued by the latter in evolution.
The central sulcus (C.S.) runs downwards and forwards in a gently curved or sinuous manner. If it passes at all on to the mesial surface of the brain, it only does so for a very short distance. Its lower end, which may be bifid, usually stops short of the Sylvian fissure ; but a narrow groove continues it into the latter oceasionallv. On the frontal lobe in front of the central
sulcus there is a short superior frontal sulcus (S.F.S.), and the sulcus arcuatus iS.Aj and sulcus rectus (S,E.) are conjoined to form a long horizontal sulcus or a triradiate sulcus.
The surface of the parietal lobe is occupied by a more or less complex system of intraparietal sulci (I.P.S.). And it appears that there are individual peculiarities in their distribution and arrangement. The system may include the sulcus postcentralis superior of Cunning-